This invention relates to electrooptical devices and more particularly to electrooptical scanning devices of the total internal reflection (TIR) type adapted specifically for beam or spot scanning.
Electrooptical devices have progressed in the art to provide a myriad of structures that operate on an electrooptic effect in a crystalline waveguide medium. Voltages are applied to an electrode array on the surface of the medium. These applied voltages cause the formation of a phase pattern in the medium which deflects and/or focuses the light wave propagating through the medium. This phenomenon occurs because an electric field, established in the medium by the voltages applied to the electrodes, varies the index of refraction of the medium sufficiently to change the relative phase of portions of the light wavefront as it propagates through the medium.
One type of electrooptic medium is the bulk electrooptic modulating device wherein the light wave is confined to a bulk crystal of electrooptic material with an applied electrode array, as illustrated in U.S. Pat. Nos. 3,517,200 and 3,787,111. Another type of electrooptic medium in the form of a thin film waveguide with an applied electrode array, as illustrated in U.S. Pat. No. 3,887,885 and on page 55 of the periodical, "Physics Today", the May 1976 issue. The electric fields required to generate a periodic index of refraction variation may be applied by electrodes disposed on opposite major surfaces of the electrooptic medium to produce these fields transversely across the medium, as illustrated in the above-mentioned patents. The electric fields may also be applied from electrodes disposed on one major surface of the electrooptical medium by employing two sets of interleaved electrodes, also referred to as interdigital electrodes, that produce fringe electric fields into a major surface of the medium.
In either case, the electric fields established in the medium are employed to produce an electrooptic effect to shape the phase front of the oncoming light wave.
Recently, total internal reflection (TIR) modulating devices have come into prominence and attention. In these devices, a set of interdigital electrodes are employed on a major surface of the electrooptic medium to induce fringe electric fields into the electrooptic medium and interaction of the light beam with these fields which is assured by the grazing internal reflection of the light beam off the major surface. Examples of TIR modulators are disclosed in U.S. Pat. Nos. 3,958,862 and 4,125,318, these patents being assigned to the assignee herein.
More recently, it has been suggested to individually address an alternate set of electrodes. Voltages are applied to one set of electrodes while the other set of electrodes remain at a reference voltage level, such as, ground, to produce a phase modulation of the light beam at the location of each addressed electrode. By applying a voltage difference to a pair of electrodes, the local magnitude of the electrical fringe field between them can be controlled and varied to permit deflection of the light to a predetermined point at an image plane. For this purpose, a Fourier transform filter and imaging lens are necessary to produce a focused spot at an image plane. With proper voltage modulation across the electrodes, i.e., by addressing the electrodes in a sequential manner across the electrode array, and applying diffraction pattern filtering, a scanning spot may be produced across the image plane. These principles are disclosed in Ser. No. 040,607 filed June 21, 1979, now U.S. Pat. No. 4,281,904 and assigned to the assignee herein and entitled "TIR Electrooptic Modulator With Individually Addressed Electrodes".